Windows enhance the natural daylighting but bring in the glare. To reduce or minimize the glare, the mini blind, curtain and drape have been invented and applied. Window fails as a light shelf. Hence, architect applies additional light shelves to improve the daylighting distribution in a building, and it increases the electric energy cost. To avoid the additional light shelves and energy cost, we need an integrated window/light shelf system without glare.
Also, for the winter solar heating, windows with high transparent, anti-reflective film between two glass panes are located along the south wall. To reduce the summer solar heat gain and lower the summer cooling load, windows with an exterior, tinted or selectively absorbing pane are used. The needs of windows for the summer and winter are opposite and impose a conflict to each other. Can the same window serve both needs?
A natural way to eliminate the glare is to reduce the sun light intensity. To provide the illumination simultaneously, the remainder of the sun light needs to be transmitted. For the variation of solar and climate conditions, the system must provide a range of transmittance and shading coefficient. Hence, a window and a blind-like, light reflective/low transparent glass plate unit should be integrated to control the sun light intensity. To meet the needs of being a solar heat transmitter in the winter and a solar heat reflector in the summer, the reflective glass unit must be able to open and close by a control device. Such an idea leads to this invention.
1. Field of Invention
This invention relates to a field of systems and products for passive solar energy and building applications. These applications include the solar cooling load reduction in the summer, the solar heating in the winter, and daylighting distribution for the illumination to reduce the light shelves and electric energy.
2. Description of the Prior Art
The paper, "Turning Low Solar Heat Gain Windows into Energy Saving in Winter", were presented by D. Feuermann and A. Novoplansky of Ben-Gurion University of the Negev, Sede Boker Campus, 84990 at the ASES' 21st National Passive Solar Conference at Boulder, Colo. in 1996. The reduction in summer peak cooling loads of buildings is often achieved by windows with a low solar heat gain coefficient. These windows are typically doubled glazed with the exterior pane tinted or selectively absorbing. Absorbed solar radiation is rejected to the environment. This is undesirable in the cold season. The authors suggested to turn south facing windows by 180.degree. for the duration of the cold season. Through the computer simulation, they had estimated seasonal energy savings for a model room in several climates. Windows whose positions are designed to be reversible are commercially available for ease of cleaning. These rotatory windows will serve the solar heat source in the winter and the summer cooling load reduction simultaneously. However, these windows are not designed to serve the purpose of eliminating the solar glare while providing the daylighting for the building illumination.
Commercially, there are numerous designs and products of mini-blind, drapes, curtains and shutters to control and eliminate the glare. However, they mostly block the glare. They may allow the glare to leak through and present part of the bad effect from the glare. Light shelves are used to compensate the illumination. The problem of mini-blind for a window to function as a light shelf is that the blade material is typically plastic and non-transparent. Sun light and glare are blocked rather than controlled. The solar heat are absorbed by the curtain and added to the cooling load in the summer. The solar heat is reflected or blocked by the blind or shutter. The winter solar heating through a window gets lost.
The multi-purposes of a window as a light shelf with no glare, solar heating in the winter, and solar cooling load reduction in the summer have never achieved in one design. We are providing such a window/light shelf system in this invention.